Lnenicka G A, Arcaro K F, Calabro J M
Neurobiology Research Center, Department of Biological Sciences, University at Albany, State University of New York, Albany, New York 12222, USA.
J Neurosci. 1998 Jul 1;18(13):4966-72. doi: 10.1523/JNEUROSCI.18-13-04966.1998.
In cultured nerve cord explants from the crayfish (Procambarus clarkii), the normal impulse activity levels of growing motor axons determine their response to Ca2+ influx. During depolarization or Ca2+ ionophore application, normally active tonic motor axons continue to grow, whereas inactive phasic motor axons retract and often degenerate. To determine the role of Ca2+ regulation in this difference, we measured the intracellular free Ca2+ concentration ([Ca2+]i) with fura-2. Growth cones from tonic axons normally had a higher [Ca2+]i than those from phasic axons. When depolarized with 60 mM K+, growth cones and neurites from phasic axons had a [Ca2+]i three to four times higher than did those from tonic axons. This difference in Ca2+ regulation includes greater Ca2+-handling capacity for growing tonic axons; the increase in [Ca2+]i produced by the Ca2+ ionophore 4-bromo-A23187 (0.25 microM) is four to five times greater in phasic than in tonic axons, and the decline in [Ca2+]i at the end of a depolarizing pulse is three to four times faster in tonic axons than phasic ones. Blocking impulses in growing tonic axons for 2-3 d with tetrodotoxin reduces their capacity to regulate [Ca2+]i. Thus, growing tonic and phasic axons have differences in Ca2+ regulation that develop as a result of their different activity levels. These activity-dependent differences in Ca2+ regulation influence axon growth and degeneration and probably influence other neuronal processes that are mediated by changes in [Ca2+]i.
在小龙虾（克氏原螯虾）的培养神经索外植体中，生长中的运动轴突的正常冲动活动水平决定了它们对钙离子内流的反应。在去极化或应用钙离子载体期间，正常活跃的紧张性运动轴突继续生长，而不活跃的相位性运动轴突则回缩并常常退化。为了确定钙离子调节在这种差异中的作用，我们用fura-2测量了细胞内游离钙离子浓度（[Ca2+]i）。紧张性轴突的生长锥通常比相位性轴突的生长锥具有更高的[Ca2+]i。当用60 mM K+去极化时，相位性轴突的生长锥和神经突的[Ca2+]i比紧张性轴突的高3至4倍。这种钙离子调节的差异包括生长中的紧张性轴突具有更大的钙离子处理能力；钙离子载体4-溴-A23187（0.25 microM）引起的[Ca2+]i增加在相位性轴突中比在紧张性轴突中大四至五倍，而去极化脉冲结束时[Ca2+]i的下降在紧张性轴突中比相位性轴突快三至四倍。用河豚毒素阻断生长中的紧张性轴突的冲动2 - 3天会降低它们调节[Ca2+]i的能力。因此，生长中的紧张性和相位性轴突在钙离子调节上存在差异，这些差异是由它们不同的活动水平导致的。这些依赖于活动的钙离子调节差异影响轴突的生长和退化，并且可能影响其他由[Ca2+]i变化介导的神经元过程。
